A small metal ball thrown vertically upwards from the top of a tower with an...

PHYSICS
JAMB 1991

A small metal ball thrown vertically upwards from the top of a tower with an initial velocity of 20ms-1. If the ball took a total of 6s to reach ground level, determine the height of the tower [g = 10ms-2]

  • A. 60m
  • B. 80m
  • C. 100m
  • D. 120m

Correct Answer: A. 60m

Explanation

Time from tower to top, t = \(\frac{u - v}{g}\)

= \(\frac{20 - 0}{10}\)

= 2s

distance from tower to top

x = ut - \(\frac{1}{2}\)gt2

= (20 x 2) - (\(\frac{1}{2}\) x 10 x 2 x 2)

= 20m

Time from the top to the ground, t = 6 - 2

= 4s

distance from top to ground,

x = ut - \(\frac{1}{2}\)gt2

= (0 x 4) + (\(\frac{1}{2}\) x 10 x 4 x 4)

= 80cm

therefore, height of tower = 80 - 20

= 60m



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